1. Field of the Invention
The present invention relates to a loop antenna attached to a rear window of a vehicle, more particularly relates to a loop antenna able to be installed on the rear window of a vehicle provided with a defogger, a method of mounting a loop antenna on a rear window of a vehicle, and a rear window of a vehicle provided with a loop antenna.
2. Description of the Related Art
Since the past, automobiles and other vehicles (moving bodies) have been equipped with antennas able to receive electromagnetic waves even during motion. The electromagnetic waves received by vehicles have for many years mainly been medium waves (MW) for AM radio use and very high frequency (VHF) or ultrahigh frequency (UHF) for FM radio use or television use. In recent years, GPS (global positioning system) antennas, antennas for receiving terrestrial wave digital broadcasts, and other antennas for sending and receiving high frequency band electromagnetic waves have become necessary in vehicles. Further, antennas for sending and receiving electromagnetic waves to and from beacons of electronic toll systems (ETC) and vehicle information communication systems (VICS) have become necessary in vehicles.
The location where an antenna is mounted when mounting an antenna on a moving body such as an automobile is generally the front window or rear window of the vehicle. When an antenna is mounted at the front window, the antenna is formed on a transparent film and this transparent film-like antenna is adhered to the inside of the front window of the automobile.
The adhesion of such a transparent film-like antenna at the front window of an automobile is described in for example Japanese Patent Publication (A) No. 2005-102183. The antenna described in this Japanese Patent Publication (A) No. 2005-102183 is an integrated antenna comprised of a transparent film formed with a GPS antenna, satellite digital broadcasting antenna, ETC antenna, TV broadcasting antenna, etc., that is, comprised of a film on which a plurality of antenna elements are formed by conductive ink, conductive foil, etc.
On the other hand, when an antenna is mounted on the rear window, the antenna is mostly placed at the rear window or the rear body at the rear of the vehicle. As the antenna in this case, a pole antenna is generally used. This reason is that the rear body of a vehicle is made of metal. The rear window is provided with a defogger comprised of electrical heating wires for defogging, so these end up having an effect on the reception of the electromagnetic waves. This makes mounting a sheet-like antenna there difficult.
However, a pole antenna installed at the rear body of a vehicle or the rear window sticks out from the body of the chassis, so ruins the appearance and therefore is not preferable design wise. Further, even if trying to set a film antenna at the rear window, it ends up being affected by the electrical heating wires of the defogger. In particular, digital TV broadcasts are horizontally polarized waves. The electrical heating wires of the defogger are arranged in the horizontal direction, so the defogger blocks the electromagnetic waves of the digital TV broadcasts. A film antenna adhered to the inside of the passenger compartment therefore has difficulty receiving the electromagnetic waves of digital TV broadcasts.